The present application claims priority under 35 U.S.C. xc2xa7 119 of German Patent Application No. 198 55 940.2, filed on Dec. 4, 1998.
1. Field of the Invention
The invention relates to a process as well as a system for drying a fibrous material web, in particular a paper, tissue, or cardboard web.
2. Discussion of Background Information
Currently, fibrous material webs are dried by guiding them over heated cylinders. This technique is expensive in terms of space requirements and energy consumption. Additionally, it has the disadvantage of producing an uneven distribution of moisture laterally across the fibrous material web. In order to correct this moisture cross profile, conventional techniques employ additional moistening or heating steps which are applied to particular zones of the web. Many techniques even involve heating by induction through the use of infrared emitters or by employing steam. However, these corrective measures have produced unsatisfactory results and they suffer from their own disadvantages, such as an inability to heat relatively large zone widths; an inability to control heating at precise zones such as boundaries; and an inability to deliver heat efficiently as a result of their low energy transmission density. In addition, there is the danger of fire associated with, for example, infrared emitters. Finally, they all suffer from high energy use in terms of how much heat actually reaches the web and the moisture contained therein.
The invention is directed to a process and a system for drying a fibrous material web more efficiently. Such a process and system should ideally conserve space and have favorable efficiency in terms of delivering heat to where it is needed. It should also permit a high energy density to be transmitted to the web. Finally, it should afford control in delivering heat to specific zones on the web so as to positively influence the moisture cross profile of the web.
The invention includes subjecting the fibrous material web to laser radiation whose frequency is preferably set so that the laser radiation is mostly absorbed by the water or moisture of the web so that little of this energy is absorbed by the other components of the fibrous material web.
Laser radiation permits a high energy density to be transmitted and delivered to small and precisely defined zones on the web. This ability allows for controlling the moisture cross profile, across the fibrous material web. Moreover, all the drying can take place in a single stage of production if desired, rather that in multiple steps.
Since a significant portion of the energy is absorbed by the moisture, the efficiency is improved considerably. Furthermore, such a design allows for the more simplified delivery of greater amounts of heat without the danger of damaging the web. This is done simply by adjusting the laser radiation output so as to produce higher energy densities. One disadvantage of conventional drying via heated cylinders is that, as the moisture decreases, there is a corresponding drop in efficiency. However, the invention is essentially immune from this since if there is less moisture than less heat is absorbed by it. As a result, excessive heating of the web material itself is prevented.
If necessary however, some heating of the fibers may also be acceptable. In this case the range of suitable frequencies may be broadened and tailored to the needs of the particular web.
In order to influence the moisture cross profile, the intensity of the laser radiation should be controllable zone by zone and cross-wise (laterally) to the fibrous material web. To this end, it is advantageous for the area which is influenced by the laser radiation to be controllable in any number of directions. Precise control across and along the web length is specifically desired, since doing so permits an increase or change in the power to be transmitted while maintaining a constant energy density area.
The invention also provides for limiting the laser radiation to particular regions of the fibrous material web, for example at the edges. Thus edges of a web which are particularly wet may be subjected to greater drying in these zones. The system should also have the ability to control each laser in the array individually and independently. Moreover, system should also have the ability to turn off the laser when it is detected that the fibrous material web is torn.
In order to realize the control of the laser radiation by zone by zone, it is necessary at least to fix several lasers across the width of the fibrous material web. These should be arranged side by side and laterally to the fibrous material web in the form of an array.
The system may furthermore be used on free draws for delivering a high energy density as well as a relatively uniform action of the fibrous material web. This can be provided by arranging the lasers on both sides of the fibrous material web.
In order to protect the surrounding area, in particular the working area of operating personnel, the system should include shielding. Furthermore, if the lasers are set to produce non-visible laser radiation, then the system should also include at least one visible light source in a line with these non-visible lasers so that their operation can be observed. Such sources may be positioned in any number of locations. Moreover, they ay also be used to control the direction of the lasers.
According to one aspect of the invention there is provided a process for drying a fibrous material web including guiding the fibrous material web and subjecting the fibrous material web to laser radiation. The web may be one of a paper, tissue, and cardboard web. The frequency of the laser radiation may be set so that a moisture content of the fibrous material absorbs more laser radiation than the other components of the fibrous material web. The subjecting may also include separately controlling by zone a laser radiation intensity laterally across the fibrous material web. Moreover, the subjecting may further include controlling an area influenced by the laser radiation in a longitudinal direction of the fibrous material web. The reach of a radiated area of a zone may also be controlled laterally to the fibrous material web.
The invention also provides a switching off the laser radiation when a tear in the fibrous material web is detected, the subjecting to occur predominantly at an end of a drying process, and wherein the subjecting results in evening out a moisture cross profile of the fibrous material web.
According to another aspect of the invention there is provided a process for drying web which includes guiding a web having a moisture content and subjecting the web to laser radiation to remove at least some portion of said moisture content. The web may be one of a paper, tissue, and cardboard web. The process may further include continuously guiding the web and continuously subjecting the web to laser radiation. The process may also include determining the moisture content and controlling the laser radiation in response to this determining. The process preferably provides for heating the moisture content to a greater extent than the web and the heating reduces the moisture content.
The process may also provide that laser radiation is infra-red radiation, preferably the laser radiation is set to a wavelength of at least one of approximately 1.92 xcexcm, 1.60 xcexcm and 1.48 xcexcm.
The process also provides for the subjecting being performed by an array of lasers arranged laterally across a portion of the web. The array may have the form of a plurality of lasers arranged in a row. Each laser in row may be individually and independently adjusted. The adjusting may correspond to a frequency of radiation emitted and/or to discontinuing the laser radiation. The process may also provide for a controlled amount of radiation to at least one longitudinal zone of the web. Alternatively, the process may provide for a controlled amount of radiation to a plurality of longitudinal zones of the web. The process may further include varying the controlled amounts so that different zones of said web receive different amounts of radiation.
The process also contemplates detecting a tear in the web and stopping the subjecting in response to this detecting. The process may further include preventing the laser radiation from impacting objects other than said web.
According to another aspect of the invention the process further includes measuring a moisture content of the web, communicating the measuring to a control device, and adjusting the subjecting with the control device. The measuring may further include providing a controlled amount of laser radiation to at least one longitudinal zone of the web.
In yet another aspect of the invention there is provided a device for drying a fibrous material web which includes a number of lasers arranged next to one another laterally to the fibrous material web which are fixed in relation to the fibrous material web. The device may have a number of lasers arranged on both sides of the fibrous material web. A shield may be located in a region of the lasers for shielding lasers. Moreover, at least one visible light source may be arranged adjacent the number of lasers.
The invention also provides for a system for drying a web which includes at least one laser, moisture measurement device, and a control device. The control device being capable of receiving input from the measurement device and influencing the at least one laser. The control device may control a laser radiation output of the at least one laser. The control device may further control an array of lasers. The at least one laser may produce infra-red laser radiation, preferably the laser radiation is set to a wavelength of at least one of approximately 1.92 xcexcm, 1.60 xcexcm and 1.48 xcexcm.
The system may allow the control device to adjust the laser radiation emitted by the at least one laser in response the measuring device. Furthermore, the at least one laser may be an array of lasers, wherein the array is arranged laterally across a portion of the web. Alternatively, the at least one laser may be a first laser arranged on one side of the web and a second laser arranged on another side of the web. Additionally, the first laser and said second laser each may be an array of lasers. Moreover, each array may be arranged laterally across a portion of the web.
The system may also have a radiation shield arranged adjacent the web for preventing an escape of laser radiation. At least one visible light source may also be arranged adjacent the at least one laser. Alternatively, the at least one visible light source may be arranged adjacent the array.
The invention also provides for a process for drying a fibrous material web which includes continuously guiding a fibrous material web having a moisture content, measuring the moisture content, communicating the measuring to one of a control device and an array of lasers, and subjecting the web to a controlled amount of infra-red laser radiation in order to reduce the moisture content, monitoring the web for tearing so that the laser radiation is discontinued when a tear is detected. The laser radiation may be set to a frequency range which in which more energy is absorbed by the moisture than by the web.
According to another aspect of the invention there is provided a system for drying a web which includes a control device, a plurality of lasers arranged in an array across a width of the web, a measurement device for determining a moisture content in the web, such that the measuring device coupled to one of the control device and the laser array, a shield for preventing escape of laser radiation, and a device for detecting a tear in the web. The system provides for the control device to influence a laser output of the array in order to produce a change in the moisture content of the web, such that the laser radiation is set to a frequency range which in which more energy is absorbed by the moisture than by the web.
Other exemplary embodiments and advantages of the present invention may be ascertained by reviewing the present disclosure and the accompanying drawing.